CHAPTER VII

ESTIMATES OF COST

In order to estimate the cost of installing a sewage-disposal plant and of treating continuously the sewage from any residence, certain fundamental assumptions are always necessary. In the first place, the unit cost of the manual labor which forms so large a part of the total cost of construction must be known for the particular time and place, and perhaps no item in the cost of construction is so important as this. In a great many small installations it may be excluded altogether, since all the hand work required is contributed by the householder at such times as the other work of the place may allow, without any additional cost. In other places, if a money value be placed on such labor, it may be expressed in terms of the cost of a hired man whose rate of wages, paid monthly, in addition to board, would be always less than if wages were paid to day laborers living at their own homes. Again, in the southern part of the country labor may be had for $1.25 a day, whereas in the central portion of the United States it is necessary to pay $1.75 a day, and in the extreme West from $2.00 to $3.00 a day for common labor. Often, too, the working day is of different length in different parts of the country. In the estimates which follow, labor is assumed to cost $1.60 for eight hours’ work, that is, at the rate of twenty cents an hour. If, in adapting the estimates of this chapter to any particular installation, the question of labor may be neglected because of the fact that the householder will himself do all the required work, then the item of labor cost may be eliminated. If other units than those here assumed are suitable for the particular locality where any plant is to be built, then the labor item must be modified accordingly.

_Material._—The cost of material always varies very greatly in different parts of the country. This is partly because of different freight and other transportation rates between the factories where material is made up and the particular place where that material is to be used; and partly because the profits made by the middleman increase as the material gets further and further away from the centres of civilization. Thus, in a large city six-inch sewer pipe may be sold in such large quantities that the freight rate is low and the dealer is satisfied with a small profit on each foot of pipe. In the country districts the dealer sells but little, and feels that he must have a larger profit to compensate him for the expense of keeping the material on hand. Thus, six-inch sewer pipe may be had at prices ranging from six cents up to sixteen cents per running foot, depending on the store from which it is bought.

It is evident, therefore, that it will not be possible to name any unit price which will be generally applicable, and it will be necessary for any intending builder to secure from local firms the unit prices from which his own individual estimate may be made up. The following discussion, however, will indicate the items comprising the necessary estimate, and will furnish an example by which the estimate sheet can be prepared.

_Laying Sewers and Drains._—The main drain from the house to the sewage disposal plant is of five- or six-inch pipe generally, the former being sufficiently large and a little cheaper than the six-inch pipe. The latter has the advantage of size and consequent greater freedom from clogging. The cost of five-inch pipe at a store in a village of any considerable size should be ten cents per foot, and the cost of six-inch pipe twelve cents per foot.

This pipe weighs twelve and fifteen pounds per foot respectively, and, with an ordinary wagon, fifty feet of six-inch pipe, weighing about eight hundred pounds, is a load; if four trips a day are possible from the residence to the store and if the cost of the team is estimated at $4 a day, each trip will cost $1, and each foot of pipe will cost two cents more for being hauled from the store to the grounds.

In laying the pipe, cement and sand are necessary for joints. For both kinds of pipe there is required about one cubic foot of mortar for each fifty joints, the mortar being sufficient to fill the joints and to make a collar or ring outside. In order to make this cubic foot of mortar, half a bag of cement and half a cubic foot of sand will be required. The cost of the cement out of the village store is about fifty cents a bag, although in a small place it may be seventy-five cents, or even one dollar. If one were buying cement in large quantities, a price as low as thirty cents a bag might be had. If the cement is delivered in cloth bags, a rebate of ten cents a bag is usually given if the bag is returned in good condition.

The cost of sand is usually dependent upon the cost of hauling. It will require forty minutes to shovel one yard of sand into a wagon, or at twenty cents an hour it would cost about fifteen cents. The cost of shovelling sand through a screen depends upon the amount of material which has to be rejected, since only a certain proportion of the sand is available for all that is shovelled. The cost of this shovelling is again about fifteen cents per cubic yard of material shovelled, and if one-third of it is coarse gravel which has to be rejected, one and one-half yards would have to be screened for every yard of sand available, and the cost would, therefore, be twenty cents for screening, a total cost of sand in the wagon of thirty-five cents per yard. If four loads of sand can be delivered per day, with a cost of fifty cents per hour for team and driver, the sand will cost $1.35 per yard on the grounds, this amount being increased or decreased if the number of trips per day must be made less or more.

_Excavation._—The cost of excavation depends on the character of the material and on the amount of water present, the cost of pumping or bailing the latter, if in large quantity, adding materially to the cost of shovelling. The material through which the trenches are driven may vary from a sand which can be shovelled without loosening, to solid rock which must be blasted, an intermediate condition of soil being known as hardpan and its excavation costing nearly as much time and effort as rock itself. If the soil is sand, into which a shovel or spade can be pushed without any picking of the material, the cost, as already stated, will be about fifteen cents a cubic yard for shovelling, and if the excavation is in trench and not more than six feet deep, the entire trench can be excavated for seven and a half cents a lineal foot. It is very unusual, however, to have conditions so favorable that such a low price can be counted on. If the material requires picking, instead of fifteen cents a cubic yard it will cost thirty cents a cubic yard, and a trench two feet wide and six feet deep will cost fifteen cents a running foot instead of seven and a half cents. If care is not taken at the start to throw the dirt well back, it will be necessary to re-handle the dirt from the bottom of the trench, throwing it back on the pile, and this will add from five to ten cents a cubic yard, depending on what proportion of the entire excavation has to be re-handled. In the excavation for a tank, it is quite possible that the entire material may have to be re-handled and the cost thus be increased by fifteen cents a cubic yard. If the ground is very hard, as when boulders and clay are intermixed, it may require twice as much time for loosening as for shovelling, in which case the cost of digging the trench will be forty-five cents a cubic yard, or twenty-two and a half cents per lineal foot, with five or ten cents added if the material has to be re-handled.

If the material is a loose sand or gravel, the trench will probably require sheeting, that is, boards or planks on each side of the open trench with braces between, in order to prevent caving of the banks. If new lumber has to be purchased for this purpose and its cost added to the cost of excavation, an additional sum per cubic yard or per lineal foot will be added, somewhat in proportion to the total amount of excavation to be done. Finally, if the soil through which the trench is being dug contains water, it may be necessary to have one or two men continuously pumping during all the time that the excavation is going on, and this also will add to the cost per cubic yard or per lineal foot of the trench.

Refilling may be done by hand or may be done by a drag scraper at the end of a rope, so that the team of horses may be on one side of the trench and draw into it from the other side the excavated material. This costs only five cents per cubic yard. If the dirt is thrown back by hand, the cost will be that of shovelling, namely, about fifteen cents per cubic yard. If the dirt has to be tamped in the trench, the cost will then be that of another man, and backfilling will often add thirty cents a cubic yard to the cost of excavation.

As a summary, it may be said that excavation alone in earth may cost from fifteen cents to forty-five cents a cubic yard, and that backfilling may add to this from five to thirty cents a cubic yard, the entire cost, therefore, varying from twenty cents to seventy-five cents a cubic yard for excavation and backfilling together. Nor is it possible to be more definite in explaining the proper price to put on excavation since the character of the material and the nature of the excavation are of such importance in fixing that cost. If the excavation is for a tank, it is often possible to rig a derrick with a long arm on the side of the excavation and, by means of a bucket, transfer the excavated material from the hole to the bank cheaper than by repeated shovelling or by carrying out the dirt in a wheelbarrow. Wheelbarrow work is always expensive, the cost of transporting earth in a wheelbarrow a distance of fifty feet being about ten cents a cubic yard. Sometimes a horse may be used to great advantage to lift the bucket and operate the derrick in place of a hand-worked windlass, although the use of the horse is hardly worth while unless the excavation is more than ten feet deep.

The excavation for the trenches of a sub-surface irrigation system cannot be estimated on the same basis as for a larger trench. More time is required proportionally in trimming and grading the sides and bottom, so that the cost per cubic yard is much increased. Thus, while such trenches contain about one cubic foot of earth per lineal foot, and on the basis of twenty-seven cents per yard would cost only one cent per lineal foot to dig, it is probable that, under ordinary conditions, this amount would be doubled.

The cost of underdrains must be made up from the cost of the pipe used and the cost of the necessary excavation. In the bottom of artificial filter beds, the latter amounts to little or nothing. In natural filter beds, the trenches are deeper and the cost of the underdrainage depends largely on this excavation cost. The cost of the pipe varies from two to ten cents per foot, depending on the kind of pipe used and its unit cost.

_Rock Excavation._—If the trench or the place for the tank is to be in rock, the cost of excavation is much increased. The rock must be drilled and blasting powder or dynamite used to loosen the material so that it can be thrown out later by hand. In ordinary rock, a man will drill from six inches to twelve inches of hole per hour, that is, the hole will cost from ten to twenty cents per lineal foot. The depth of the hole determines the amount of rock loosened per charge. If the holes are three feet deep, about one-third of a cubic yard is loosened per hour, while if the holes are five feet deep, one cubic yard of rock is loosened per hour. This indicates at once the economical advantage of deep holes compared with shallow ones. In the first case, nine lineal feet of hole would have to be drilled in order to get one cubic yard of rock, nearly double the amount required where the hole is five feet deep. Usually the distance between the holes is made equal to the depth of the holes, although in some rock the depth can, with advantage, be made greater than that distance. If the rock is very loose and seamy, deep holes may sometimes not be warranted, because the effect of the blasting is taken up by the loose rock in such a way that the value of the explosive is not realized. Shallower holes, more frequently blasted, utilize the explosive gases more completely.

The kind of explosive which may be used varies from slow, low-power black powder to rapid, high-power nitro-glycerine, the many forms of dynamite and high-grade powder in use being combinations of nitro-glycerine with some absorbent. In most cases, ordinary blasting powder is suitable for rock excavation in small quantity. It lifts the rock rather than shatters it, and is more convenient and safe to handle. Forty-per-cent dynamite is to be recommended where the rock is very seamy so that quick-acting explosive is essential, and also where the rock is very hard, so that black powder tends to blow out the hole rather than to shatter the rock. The cost of forty-per-cent dynamite is about twenty cents per pound, and the cost of powder is about twelve cents per pound. On the average, it may be assumed that it will require one pound of the former and one and a half pounds of the latter per cubic yard of ordinary rock excavated. The cost of lifting the blasted material out of the trench will be at about the same rate as that of earth.

_Concrete._—The walls of tanks made of concrete depend for their cost upon the cost of the material and the cost of the labor involved. It is usually more economical to use gravel as the basis of the concrete if any is available, and in order that the product may be of good quality it is always best to screen this gravel, separating it into sand and stone. The proper size of screen for this operation should be not greater than one-half-inch mesh. The stone and sand can then be re-combined with the cement in the proportion of one part of cement to two and a half parts of sand to five parts of stone, this mixture making a very strong and impervious combination. The cost of this mixture depends chiefly on the length of haul for the gravel and on the natural grading of the material. If the proportions required for concrete exist naturally in the bank or stream bed from which the gravel is to be obtained, there is little or no waste involved in screening, and the only cost is that of handling the material twice. If, on the other hand, the amount of stone is inadequate, it may be necessary to waste a good deal of the fine sand and enough material has to be shovelled to produce the required amount of coarse media. Assuming that the cost of shovelling the material from the stream bed is fifteen cents a cubic yard, and that the haul is two miles, so that four trips a day are made, then the gravel can be delivered where it is to be converted into concrete at a cost of one dollar for hauling and thirty cents for shovelling, while if the haul is only one mile, so that eight trips a day can be made, the cost will be eighty cents per cubic yard. If any waste of gravel is necessary, these costs will be increased correspondingly.

At the site of the proposed plant the sand and gravel must be mixed with the cement and carried to place. It has been found by experience when the mixing is done thoroughly and by hand, and when the resulting concrete can be shovelled directly behind the forms, that the cost of the mixing and placing is about one dollar per cubic yard of concrete. If the concrete has to be wheeled into place this cost will be added to.

In order to make a cubic yard of concrete, it is necessary to have nearly one cubic yard of the coarse material, whether this be rounded stones from a gravel bank or angular stones from a stone-crusher. Seven-eighths of a cubic yard of stone may be safely considered as necessary for a cubic yard of concrete. To this must be added three-eighths of a cubic yard of sand for a one to two and a half to five mixture. When this amount of stone and sand have been thoroughly mixed together, four and a half bags of cement should be added. Inasmuch as the variation in sizes of the individual particles of rounded gravel is such that a dense concrete results naturally, it is quite reasonable both to increase the amount of stone and decrease the amount of cement if that variation in size seems to be one which will produce a dense mixture. Thus one cubic yard of stone, one-third cubic yard of sand, and four bags of cement may be used and will, under favorable conditions, result in a good concrete. In order to determine whether this latter combination is permissible on any particular piece of work, a test may be made by thoroughly mixing the materials together in the proportions named and testing the volume of this mixture (B) in a box of measured dimensions. Then the same volumes mixed together in the former proportions (mixture A), and tested in the same box will show the relative value by occupying either more or less space than the other mixture (B). If less, mixture A is a better one, and should be used; if more, then the latter mixture, B, is the better one.

The amount of water required for mixing concrete depends upon the temperature of the outside air as well as upon the personal ideas of the person in charge of the mixing. Some builders like wet concrete and some like dry concrete. It should be noticed, however, that wet concrete is cheaper because it requires little or no tamping. Wet concrete, however, should be spaded, that is, a spade forced down into the mixture, particularly against the forms, so that particles of air caught between the stones may escape, and so that there may be no pockets between the stones into which the liquid cement mixture does not penetrate. It is generally considered that about fifteen per cent of the volume of concrete is the necessary volume of water for the mixture. This amounts to thirty gallons, or a barrel of water, to a yard of concrete, although the sizes of barrels vary, and a cement barrel would not be large enough, and a road-oil barrel would be too large.

The cost of forms depends, again, on the cost of material and on the cost of labor. Rough lumber varies in price from twenty to forty dollars a thousand feet, board measure, delivered on the grounds, and the cost of framing and placing it varies from eight to twenty dollars per thousand, depending on the skill of the carpenters and on their daily wages. In order to estimate the cost of the lumber required for building false work, it is best to determine exactly the amount of lumber required, and get the price from a lumber yard on that quantity. Ordinarily, it is safe to say that a carpenter in building forms will be able to saw and nail in place 250 board feet per day, so that, knowing the amount of lumber to be used and the wages of the carpenter, it will be easy to determine the cost of the forms as first set up. They may be taken down and removed for the purpose of re-assembling in another place for about half the cost of placing originally, and by carefully arranging to build the forms in panels or sections, they may be removed by a carpenter at the rate of 4,000 or 5,000 board feet per day.

_Valves._—In connection with a sewage-disposal plant, valves are essential at many points. At the entrance to the several parts of the settling tank, flap valves are suitable to admit or keep out sewage from the several compartments. Gate valves are used on the by-pass lines and on connecting lines between the tank and the filter beds in order to be of service when it is occasionally necessary to clean the beds. More simple valves may be used in manholes where a diversion of the flow is required and where perfect and complete water-tightness is not essential. These valves may be made of plank, sliding up and down in grooves left in the concrete walls for that purpose. Sludge valves may be made to fit in the bottom of the tank, and depend for their water-tightness on the weight of the valve itself with the aid of a rubber packing which is placed between the valve and its setting. The cost of these various kinds of valves cannot be given exactly, since their cost depends upon freight and profit of the various commission men through whom the valves are ordered, but, generally speaking, they will be found to differ but little from the costs given in the following table:

TABLE

Flap valve as shown in Fig. 16 $5.00 Gate valve (iron bearings) for 6–inch pipe (Fig. 13) 20.00 Gate valve (bronze bearings) for 6–inch pipe 30.00 Sludge valve as shown in Fig. 10 4.00 Iron slide valve as shown in Fig. 11 15.00

_Dosing Devices._—Dosing devices referred to in Chapter III are usually purchased directly from the manufacturer, and while their cost varies a little, depending upon the cost of freight, an ordinary single automatic siphon may be estimated at $15, the difference in price varying a little with the different makes of siphon. If an alternate discharge is required, then two siphons must be installed, by means of which alternate intermittency is secured, the variation, however, being only from one to the other and back again to the first. If a plural alternate discharge is to be used, the cost may be estimated roughly for a 6–inch siphon at from $50 to $75 for each unit, this price including the necessary piping but not the cost of setting.

_Filling Material._—Artificial sand filters require a sand of uniform size and one free from dirt. These two requirements add very materially to the cost of sand, since it is almost impossible to find a natural sand which fulfils the necessary requirements. A few sections of the country are fortunate in having sand in the vicinity suitable for filtration purposes without any washing or screening. Such parts of the country, however, are limited to those where sand has been deposited by glacial action, and is essentially silicious in character. It is hopeless to expect to find suitable sand in the centre of New York State, for example, and even with washing and screening, sand in this locality is far from being desirable. It will be found, further, that after this undesirable sand is washed and screened the cost of the final product is so great that it is usually cheaper to use broken stone either as a filter or as a contact bed.

Washing sand in small quantities is done by throwing the sand into a channel through which water is passing, the sand being retained by a series of low partitions in the channel. If the water enters the box or channel through a pipe at the bottom, frequent entrance holes being provided along the sides and bottom of this pipe, the sand is kept in a state of suspension, the dirt more readily washed out, and a much smaller amount of water used. The cost of shovelling the sand into the washer and again out of the washer, about thirty cents per cubic yard, must be added to the original cost of the sand. The cost of water, if pumped by hand or by steam, will be about ten cents per cubic yard of sand cleaned, making the total cost about forty cents per cubic yard. If only three-fourths of the unwashed sand is available for use, then the cost of the final product is a little less than fifty cents per cubic yard. The sand before being brought to the washer will have been sifted at an additional cost of perhaps thirty cents per cubic yard. Hauling from the bank to the washer, or from the washer to the site of the disposal works, or both, if the water supply requires the washer to be placed at some distance from the sand bank, will add from fifty cents to one dollar a yard to the costs already indicated. It may generally be assumed that it will be impossible to put sand into an artificial filter for less than $1.50 a cubic yard, and it may easily cost $2.50 a yard if the sand bank is at considerable distance from the site of the works.

Broken stone in most parts of the country can now be bought from a stone-crushing plant. If road construction has been in progress in the vicinity, the contractor for the work has been obliged to open a quarry and set up a crushing-and-screening plant, and it will generally be possible to buy broken stone from such a contractor at about fifty cents per cubic yard. The cost of hauling and the cost of shovelling into the beds must be added to determine the cost of the stone in place. Sometimes it is cheaper to bring the stone from a distance by rail, such stone costing about $1.25 at the railroad station. Then the cost of hauling and shovelling must be added. It will be noticed that the cost of stone does not differ materially from the cost of sand, and since the amount of stone needed is only about one-quarter of the sand needed, it is generally cheaper to build a stone bed. The purification, it will be remembered, however, is decidedly inferior.

_Finishing._—There is always some slight expense necessary in finishing and cleaning up after any piece of construction work. Material left over has to be hauled away, and in order to leave the plant in an attractive dress, seeding or sodding the earth slopes is desirable. It is even desirable to plant shrubbery around the edges of the beds, partly as a screen and partly to minimize the offensive suggestions which seem to be inseparable from any plant dealing with sewage. The cost of these final improvements may be as little or as much as the owner and builder chooses, but it is urged that their value should not be overlooked.

The following table is given as a guide and help in putting together the various items that make up the total cost of a sewage-disposal plant. Each line should be carefully considered, and if the item mentioned is to be used or paid for, the amount in the last column should be filled out.

TABLE OF ITEMS ON WHICH TO BASE ESTIMATE OF COST OF SEWAGE-DISPOSAL PLANT ═══════════════════════════════════════════════════════════╤═════╤═════ │ No. │Cost │ of │ │Units│ ───────────────────────────────────────────────────────────┼─────┼───── │ │ _Excavation and Refilling_ │ │ │ │ Trenches in sandy soil, shallow at per cu. yd. │ │ depth │ │ Trenches in stiff soil, shallow at per cu. yd. │ │ depth │ │ Trenches in sandy soil, deep cut at per cu. yd. │ │ Trenches in stiff soil, deep cut at per cu. yd. │ │ Tank, depth and soil duly at per cu. yd. │ │ considered │ │ Beds, depth and soil duly at per cu. yd. │ │ considered │ │ Embankments between filter beds at per cu. yd. │ │ (additional cost) │ │ Trenches for sub-surface lines at per lin. ft. │ │ Trenches for underdrains at per lin. ft. │ │ Trenches for sludge disposal at per lin. ft. │ │ │ │ _Surfacing and Finishing_ │ │ │ │ Surface soil placed at per sq. yd. │ │ Gravel in walks at per sq. yd. │ │ Flowers and shrubbery Total amount │ │ │ │ _Concrete Work_ │ │ Manholes on pipe lines at each │ │ Settling tank, bottom, sides and at per cu.yd. │ │ roof │ │ Dosing tank, in addition to at per cu. yd. │ │ settling tank │ │ Manholes on sub-surface lines at per cu. yd. │ │ Concrete in contact beds or at per cu. yd. │ │ filters │ │ Concrete in protection wall at end at per cu. yd. │ │ of outfall │ │ │ │ _Pipe Lines_ │ │ │ │ 5– or 6–inch tile pipe (laid), at per lin. ft. │ │ house to disposal plant │ │ 6–inch pipe used in disposal at per lin. ft. │ │ plant, laid │ │ 6–inch pipe from plant to outfall at per lin. ft. │ │ 6–inch pipe for sludge line at per lin. ft. │ │ 6–inch pipe for main underdrain at per lin. ft. │ │ 3–inch agricultural tile in at per lin. ft. │ │ sub-surface disposal │ │ 4–inch agricultural tile in at per lin. ft. │ │ underdrains │ │ 6–inch specials, bends, tees, at each │ │ etc., in addition to cost of │ │ straight pipe │ │ 3–inch specials, bends, tees, at each │ │ etc., in addition to cost of │ │ straight pipe │ │ Cast-iron pipe at per lb. │ │ Cast-iron specials, bends, etc. at per lb. │ │ Wooden troughs for surface at per 1000 ft. B.M.│ │ distribution, in place │ │ │ │ _Filter Material_ │ │ │ │ Gravel filling around sub-surface at per cu. yd. │ │ tile, placed │ │ Sand filling for artificial filter at per cu. yd. │ │ beds │ │ Broken stone for contact beds or at per cu. yd. │ │ for filters │ │ Broken stone for sludge beds at per cu. yd. │ │ │ │ _Valves_ │ │ │ │ Gate valves, Fig. 13 at each │ │ Flap valves, Fig. 16 at each │ │ Slide valves, Fig. 11 at each │ │ Wooden slide valves at each │ │ Sludge valves, Fig. 10 at each │ │ │ │ _Tools_ │ │ │ │ Shovels, long or short handled at each │ │ Picks at each │ │ Wheelbarrows, wooden or steel at each │ │ Sieves for screening sand and at each │ │ gravel │ │ Saws, hammers, and axes Total amount │ │ │ │ _Lumber_ │ │ │ │ For sheeting and bracing; rough at per 1000 ft. B.M.│ │ lumber │ │ For forms for concrete work, sized at per 1000 ft. B.M.│ │ For runways, staging and mixing at per 1000 ft. B.M.│ │ boards, plank │ │ │ │ _Hardware_ │ │ │ │ Nails for forms, staging, etc. at per 100 lbs. │ │ Bolts or wire for concrete forms at per lb. │ │ │ │ _Iron Work_ │ │ │ │ Manhole frames and covers at per lb. │ │ Steps for manholes at per lb. │ │ │ │ _Siphons_ │ │ │ │ Flushing siphons for dosing tank at complete │ │ Timed siphons for emptying contact at complete │ │ beds │ │ │—————│————— Total │ │ ───────────────────────────────────────────────────────────┴─────┴─────

_Cost of Maintenance._—As to the cost of maintenance, very little that is definite can be said. Sub-surface irrigation plants should require no expenditure except for the occasional cleaning of the sedimentation tank. If this is emptied three times a year, the labor needed would amount to about a half-day’s time on each occasion for a family of ordinary size. For sand filters, either natural or artificial, the tank must be emptied as with sub-surface irrigation, and, in addition, the surface must be scraped occasionally, and at the approach of winter furrows must be dug. Perhaps two days’ time would be all that would be needed for a plant dealing with the sewage of a single family. A broken-stone bed requires no attention for seven or eight years, and then the stone has to be shovelled out, washed, and replaced.

In none of the installations is this excessive in comparison with the benefits received, and it should not be considered a burden to expend this amount of time in maintaining so important a part of the household economy as the disposal of the household wastes in a sanitary manner. It must not be forgotten, however, that no sewage-disposal plant is exempt from occasional break-down or accidents, and that there must be a constant supervision exercised. This supervision should not require much more time than above suggested, but should be exercised for the purpose of correcting irregular flows or distribution before the value of the plant is utterly destroyed.

INDEX

Bacteria, action of, in reducing organic matter and sewage, 6

Baffle boards in settling tank, 30

Broad irrigation, 98 areas, maintenance of, 108 methods of applying sewage in, 104 sewage disposal by, area required, 102 when advisable, 110

Clay soils for sewage purification, 9

Cleaning settling tanks, 32

Composition of sewage, 4

Concrete for walls and floors of settling tanks, 24 walls, forms for constructing, 22

Contact beds, 87 alternating flow to, 89 general features of construction of, 89 principles involved, 88 table for use in constructing, 92 underdrainage of, 89

Cost items of sewage-disposal plant, table on which to base estimates, 125

Cost of broken stone, 124 of concrete, 119 of dosing devices or siphons, 122 of excavating and refilling, 115 of finishing and cleaning up, 124 of forms for concrete walls, 121 of laying sewers and drains, 113 of maintaining sewage-disposal plants, 127 of material, 113 for filter beds, 123 of rock excavation, 117 of sand, 114 of sewage-disposal plants, 112 of valves, 122

Crops, yield of, with and without sewage irrigation, 103

Disease, transmission of, by insects, 1

Dosing apparatus, Ansonia automatic, 43 three kinds of, 53

Drain pipe from settling tank, 26

Emscher or Imhoff tanks, 34

Excavation for settling tanks, 25

Fertilizing elements in sewage, value of, 98

Forms for building settling tanks, 22

Grease traps in connection with sand filters, 78

Imhoff or Emscher tanks, 34

Irrigation, amount of water necessary for, 101 of orchards, 108 value of sewage for, 99

Laws against disposal of sewage into streams, 3

Manholes through settling-tank roof, 29

Overflow pipe from siphon chamber, 31

Roof of settling tank, construction of, 27

Sand filters, alternating flow of effluent to different beds composing, 83 artificially constructed, 79 details of construction of, 74 devices for dosing, 82 distribution of effluent over, 78 preparation for winter of, 84 quality of sand suitable for, 86 scraping surface of, 84 settling of sewage before application to, 77 table for use in constructing, 76 underdrainage of, 81

Sand filtration, 74

Screening of sewage, 5

Settling-tank floors, necessary slope of, 26 tanks compared with septic tanks, 11 construction of floors of, 25 description of, 16 dimensions for, 18 function of, 14 location of, 20 near sub-surface irrigation field, 31 materials for and construction of, 20 operation of, 32 partial treatment only provided by, 16 water-tight, construction of, 24

Sewage, composition and character of, 4 disposal—an engineering problem, 1

Sewage disposal: by dilution, 3 in soils, three essential conditions for, 8 need of, 2 plants, permissible rates of operation of, 8 preliminary and final methods of, 11

Sewage filters, 73 proper operation necessary to success of, 96 relative efficiency of various types of, 73

Sewer, size and gradient of effluent, 63, 77

Siphon chamber, depth of sewage in, 38

Siphon chambers, 21, 60 necessity for, 37

Siphon, Miller, 45 simplest form of, 44 Van Vranken, 44

Siphons, alternating air-lock, 52 discharging depth or draught of, 77 for automatic discharge of sewage effluent, 42 how to place, in position, 25, 64, 77 Merritt, 50 placing two in one chamber for alternating flow, 47 plural alternating, 48 sketches of and directions for setting furnished by manufacturers of, 53

Size of dose in disposal plants, 10

Sludge pipe from settling tank, 27

Soils and their suitability in purifying sewage, 7

Sprinkling filters, 93 construction and operation of, 94

Sub-surface irrigation, conditions favorable to, 71 description of, 55 fields, location of, 58 soils suitable for, 57 special advantages of, for country home, 57 system—advantages over cesspools, 56 systems, alternate use of different portions of, 68 details of construction of, 58, 63 value of underdrainage in, 69 tables for use in constructing, 59 underdrains for, 69

Sub-surface tiling, depth below ground surface of, 67 gradient or fall of, 67 how to lay, 64 necessary length of, 66

Timed siphons for discharging contact beds, 91

Valves, English slide, 40 flap attached to sewer pipe, 41 with loose-link hinges, 42 with metallic seat, 41 hand, 39 ordinary gate, 40 sluice gate, 40

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ARRANGED UNDER SUBJECTS

Descriptive circulars sent on application. Books marked with an asterisk (*) are sold at net prices only. All books are bound in cloth unless otherwise stated.

AGRICULTURE—HORTICULTURE—FORESTRY.

Armsby’s Principles of Animal Nutrition 8vo, $4 00

* Bowman’s Forest Physiography 8vo, 5 00

Budd and Hansen’s American Horticultural Manual: